<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box {
            width: 1000px;
            height: 400px;
            margin: 50px 0px;
            border: 1px solid black;

        }

        .box div {
            margin-right: 30px;
        }

        .son:nth-child(1) {
            width: 200px;
            height: 200px;
            background-color: burlywood;
        }

        .son:nth-child(2) {
            width: 200px;
            height: 200px;
            background-color: red;

        }

        .son:nth-child(3) {
            width: 200px;
            height: 200px;
            background-color: blue;
        }

        .box1 div {
            float: left;
        }

        .box2 {
            justify-content: start;
            align-items: baseline;
            display: flex;
        }
    </style>
</head>

<body>
    <p>以前的布局方式</p>
    <div class="box box1">
        <div class="son"></div>
        <div class="son"></div>
        <div class="son"></div>

    </div>
    <p>弹性盒交叉轴对齐方式</p>
    <div class="box box2">
        <div class="son"></div>
        <div class="son" style="height: 250px;border: 10px solid black;font-size: 50px;">XXxx</div>
        <div class="son"></div>

    </div>

</body>

</html>